In order to deploy an airbag at the time of collision of a vehicle, a load sensor is provided between a seat cushion of a vehicle seat and a vehicle floor, a load body acting on the vehicle seat is determined on the basis of the load detected by the load sensor and, for example, when it is determined that an adult is seated on a vehicle seat for a passenger seat, the airbag is brought into a deployment-allowed state, and when it is determined that there is no passenger on the vehicle seat or when it is determined that a child is seated, the airbag is brought into a deployment-disabled state.
For example, when the vehicle engages in a light collision, a load not smaller than a predetermined value acts on the vehicle seat due to an impact generated in the vehicle, and hence a seat frame of the seat cushion may be subjected to a slight deformation. When the deformed portion of the seat frame is a portion where the load sensor is mounted, there arises a problem of occurrence of a displacement of a zero point position (a position where the detected load is zero when no load is applied) of a detection system of the load sensor followed by lowering of a detecting accuracy of the load in the vehicle seat. Generally, when the collision of the vehicle is light, a user does not bring the vehicle to a service garage and hence there is no opportunity to inspect or repair the vehicle. In such a case, a state of the vehicle seat in which the determination of the load body is not accurate due to the lowering of the detection accuracy of the load is left untouched.
In order to solve such a problem, an example of the seat load detection apparatus which is capable of notifying the passenger of necessity of inspection of the vehicle by allowing detection of a case where the vehicle engages in a light collision on the basis of a variation in detection load from the load sensor is described in JP 2011-43454 A.
In contrast, since the value of the load detected by an inclination angle of the vehicle varies, the determination accuracy of the load body is liable to be lowered and, for example, the load sensor disposed on the rear side of the seat shares a smaller rate of the load body on the seat on a downhill than the flatland, underdetection of the load may occur. Therefore, even though a passenger of the seat is an adult, the passenger may be determined as a child. In order to solve such a problem, an example of a seat load detection apparatus configured in such a manner that whether the vehicle is on a flat road or on the hill is detected on the basis of the detected load from the load sensor and, if it is determined to be on the hill, the detected load is corrected in accordance with the fore-and-aft inclination angle of the vehicle is disclosed in JP 2011-17592 A.
However, for example, determining the load body simply on the basis of a load applied on a rear portion of the seat cushion is often associated with a problem. When a posture changing apparatus configured to change the position of the seatback which corresponds to a backrest for a passenger from a first stage position which is a most upright position of a seatable position to a forwardly inclined position which is a position inclined forward, that is, a non-seatable position is mounted on the vehicle seat on the side of passenger seat in order to facilitate getting on the vehicle to a rear seat or getting out of the vehicle from the rear seat, there arises a new problem as described below. The first stage position of the seatback is set as the zero point position (where the detected load is set to be zero when no load is applied), and is generally adjusted in such a manner that the detected load becomes zero when no load is applied.
When the seatback is restored from the forwardly inclined position to the first stage position, an impact is generated when the seatback is restored to the first stage position. Therefore, the detected load is as much as that in the case where the vehicle engages in a light collision when the vehicle is traveling rearward, and hence an erroneous operation that a vehicle collision, which is not actually occurred is detected occurs even though the vehicle seat is not changed into a state in which an impact is applied to the vehicle.
In contrast, when the vehicle is on the flat road and the seatback is at the forwardly inclined position, the center of gravity of the seatback is moved forward of the seat cushion, and hence the load sensor disposed on the rear side of the seat detects a load smaller than that in the case where the seatback is at the first stage position. Consequently, an erroneous operation that the vehicle is detected to be on a downhill even though the vehicle seat is not changed to a state that requires to correct the detected load according to the inclination angle of the hill, that is, even though the vehicle is on the flat road, and the detected seating load is corrected according to the inclination angle in the fore-and-aft direction of the vehicle on the downhill occurs.
Therefore, a seat load detection apparatus configured so as not to be associated with drawbacks as described above is desired.